docs: def feat(self,subset):
          """Obtain the feature class value of the specific subset.
  
          If a feature occurs multiple times, the values will be returned in a list.
  
          Example::
  
              sense = word.annotation(folia.Sense)
              synset = sense.feat('synset')
  
          Returns:
              str or list
          """
          r = None
          for f in self:
              if isinstance(f, Feature) and f.subset == subset:
                  if r: #support for multiclass features
                      if isinstance(r,list):
                          r.append(f.cls)
                      else:
                          r = [r, f.cls]
                  else:
                      r = f.cls
          if r is None:
              raise NoSuchAnnotation
          else:
              return r